<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<ul>
    <li>1</li>
    <li>2</li>
    <li>3</li>
    <li>4</li>
    <li>5</li>
    <li>6</li>
</ul>
<script src="../jquery-1.12.4.js"></script>
<script>
    $(function () {
        //隔行变色
        $("li:even").css("backgroundColor","skyblue");
        $("li:first").css("color","white");//第一个
        $("li:eq(3)").css("fontSize","20px");//第某个，从0开始
    });
</script>
</body>
</html>